def say_hello():
    """
    打招呼
    :return:
    """
    print("hello world")
    print("hello world")
    print("hello world")

def sum(a, b):
    """
    求两个数之和
    :param a:
    :param b:
    :return: a和b的和
    """
    return a + b

def my_min(a, b):
    """
    返回两个数较小那个
    :param a:
    :param b:
    :return: 较小值
    """
    if a < b:
        return a

    return b

def calc(a, b):
    """
    计算两个数的积和商
    :param a:
    :param b:
    :return:
    """
    multiply = a * b
    divide = a / b if (b != 0) else None
    return multiply, divide

say_hello()
print(sum(10, 20))
print(my_min(10, 5))
print(calc(3, 5))
print(calc(3, 0))
